Filling in centerline letters

[Rob]

I have been trying to create a few carvings that have words carved into the design. In finishing, I want to fill in the letters so that they are easier to read. My wife has some small paintbrushes that she has attempted to fill in the letters and it always smears and doesn't look good. We have tried filling them in and then sanding over them to get any bleed from the wood surface. That doesn't work. We have attempted fine paint pens, fin markers, etc that fill in the bottom of the letter and not the edges, then they don't look and don't have the depth.

I have nearly gave up, then was in a shop a couple of weeks ago and found a project that someone else had done and now know it is doable. A pic of their project is attached.

HOW THE HECK DO I FILL IN THE LETTERS TO MAKE IT LOOK THAT GOOD - LOL?? I mean, their letters, logo, etc. looks great.